Hi bro. I won't say I'm hard-core on tanning, where I just leave the tanning light on when it's dark/night. To some people, that's not even considered tanning.
My experience was that it turned into a very good orange (borderline red? ?) after 2 months in my tank. At the LFS, it was at that time the reddest among approx 25-30 reds for sale. I would think in the particular LFS, they perform hard-core tanning and I won't be surprised if they feed them agents to bring out the red (these days they range from hormones to carotene). So I would think my method failed or it wasn't tanning to begin with.
But it is safe to say that red arowana requires constant tanning (lots of tanning lamps plus not too big a tank), so I gave up.
Sorry bro, I'm of not much help here.